Effects of various polymerization techniques on PANI deposition at the surface of cellulose ester microporous membranes: XPS and electrical conductivity studies

Polyaniline (PANI)-mixed cellulose ester (ME) composite membranes were synthesized by depositing PANI on microporous ME membranes using various in situ chemical oxidative polymerization techniques. These techniques differ in contacting patterns and addition sequence of the monomer and oxidant in the polymerization reaction which result in different PANI deposition sites in the membranes and extent of surface layering on the surface of the membrane. The extent of PANI surface layering on the base microporous membrane was characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM images show PANI coating around the fibrous strands that make the structure of the base membrane. This results in highly discontinuous and incomplete surface layering. XPS was used to study the effects of various polymerization techniques and conditions on the extent of PANI layering at the surface. Deconvolution of C 1s and N 1s spectra showed an incomplete surface coverage of the base membrane that was polymerization technique-dependent. The maximum layering extent was shown by vapor-phase polymerization. The protonation of PANI nitrogen and anion doping levels were characterized by deconvoluting N 1s and Cl 2p spectra, respectively, whereas hydrolytic degradation of PANI was studied by the deconvolution of O 1s core level spectrum. Prolonged polymerization using two-compartment permeation cell showed higher levels of PANI protonation and hydrolytic degradation. The effects of PANI deposition extent at the surface of the membranes on the electrical conductivity have been also elaborated where the conductivity values varied between 10−5 and 0.11 S cm−1 depending on the polymerization technique.